Different cam? Chain? Car should be faster
 

Seeking opinions:

My oil pan and rear main seal are leaking. So, I was going to pull the engine. I’ll need a new pan, one piece gasket and was going to do the one piece rear main seal.

While the engine is out, I was curious about making upgrades. Personally, I feel like the car is a dog for the size of the engine and the combination of parts and drivetrain. I understand that this is subjective. On my little quarter mile test tool, it will do mid 14 seconds. I feel like the car should be quite a bit faster.

I’m curious if a different cam would give me more power, without sacrificing street manners? The car currently has perfect street manners. It drives like any modern car. But, when I punch it, I’d like it to be faster. I don’t have a big desire to switch to a roller cam.

The springs are pretty old and I was thinking of going to the Crower 68404.

Also, the last time the engine was out, I feel like the timing chain had quite a bit of slack in it. Seeing as how the block has been line honed at least once, I was thinking maybe I should run one of the undersized chains?

Looking for any advice on cam, lifters, pushrods, timing chain, if there is more power to be had, without sacrificing street manners.


The car is a 67 Firebird convertible.

The engine is a 1970 455, bored .060. It’s been line honed as well.

It has a factory crank ground .010 on rods and mains.

Forged pistons and rods.

The heads are 1971 Pontiac 400 heads, Code 96. Mildly ported, stainless valves. I’ve got Comp Cams roller rockers, ration 1.52. I think they are Magnum. The springs are some tired Comp 988 springs. I was thinking of switching to the Crower 68404.

Compression Ratio should be 9.53:1.

Intake is Edlebrock Performer, port matched.

Car is a Holley 750 with vacuum secondary.

Distributer is Performance Distributors HEI, custom curved.

Trans is a 700R4 with a 2600 stall lock up converter.

Rear end is 3.73 Chevy 12 bolt.

It’s got headers and dual exhaust.

The cam is a Summit 2802.
Cam Style:Hydraulic flat tappet
Basic Operating RPM Range:2,200-5,500
Intake Duration at 050 inch Lift:224
Exhaust Duration at 050 inch Lift:234
Duration at 050 inch Lift:224 int./234 exh.
Advertised Intake Duration:298
Advertised Exhaust Duration:303
Advertised Duration:298 int./303 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.466 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.488 in.
Valve Lift with Factory Rocker Arm Ratio:0.466 int./0.488 exh.
Lobe Separation (degrees):114

Thanks in advance

Cam is too small. The experts here will give you some solid advice.

Thank you. Starting to think maybe a Ram Air 4 cam and switch to a Performer RPM intake might wake up my combo. I'm worried about this 50% failure rate on new flat tappet cams though. I really hadn't considered switching to a roller.

The 455 with 96 heads was a real popular combo in the past. Maybe search for some similar combos here. I would lean toward something like a copy of an ultradyne 288/296 cam.

is a 750 too small for that combo?

Definitely cam is to small. On the 50% failure rate. Any new hyd cam has to be checked before installing to make sure the lifters and cam has the proper taper. Because that has been a big issue.

A larger cam should let it RPM higher but the torque should be there in current form and with that crankshaft with 3.73 gears and extra low first in the trans 2600 stall .. it should be impressive at some point..
basics...check for full throttle maybe secondary vac spring is a black RV spring jetting all kinds of things

i have a 462 slightly larger solid cam 6X-8 heads th400 2.73 gears that pulled a 13.6 at 5800 DA .. so somethig is amiss if your description is accurate

This is cam you want to go with Crower 60919 cam, its basically the Ram Air 1V cam. But much better then old Ram-IV. It’ll wake that baby right up.

Here’s a few things I see.

That carb is too small for that cid motor and with that intake especially!

That intake itself might be the choke depending on how well the porting work turned out.

Keep that cam and when you get the motor back in the car add 1.65 rockers to the intakes only.

To make that work right the springs need to be changed as you have already talked about and the intake needs to be changed out to a performer rpm.

While the engine is on the stand be sure to check and see if the usage of 1.65 rockers calls for different length push rods.

And yes, even 3 degrees of unnecessary cam retard can knock 25 to 30 hp off a motor above 5000 rpm in terms of your CID.

Listen to Gach

How was the existing cam installed? Was it degreed, or was it crammed-in "dot to dot"? What is the cranking compression pressure for all eight cylinders?

That 750 carb and intake is not too small for a 455...at low RPM. If that car doesn't launch hard, it's something else. I don't know how a 700 trans can take the torque of a properly-running 455 even with "billet everything".

What is the fuel pressure after several seconds of WFO?

On my 455, I switched from the 3.73's I had in the rear to 3.36's and the car tended to pick up some. If your current combo is throwing all the torque at you very early and falling on it's face without many revs, those 3.73's are just helping you blow past the torque the engine is making. Taller gears can help you spend more time in the engine's power band, turning it into speed.

I also agree that the intake and carb are likely too small. I would switch to either a factory intake manifold or to a torker ii. It's unlikely that the Performer RPM will fit underneath the hood of your 67 firebird. It's a big engine, the single plane manifold isn't going to kill the torque.

If you're set on changing the cam while you're in there, I think pretty much everyone would lean towards that crower 60919. If you need more manners out of it, you can pair it with a set of Rhoads lifters. Just make sure that the cam and lifters are checked specifically for proper taper, runout and hardness. There's been a lot of testing on these through 2023 and hardness doesn't appear to be an issue, but cams ground with no, or improper amounts of taper as well as lifters with out of spec face machining.

If the engine has been line bored, do you know how much it took to get everything straight? If not, you may need to contact the builder and try to determine, otherwise you're guessing. Either way, try to get a timing set that uses an IWIS chain.

It doesn't. Ask torqhead about it.

Lots of good tips here. Schurkey, it was crammed in dot to dot and like I said, the chain was pretty sloppy. I'm figuring I'll instal one of those undersized ones. I run an Edelbrock electric fuel pump, the higher pressure one with a regulator, so fuel pressure shouldn't really be an issue. It should have plenty of flow.

I'm seeing recommendations for the Performer RPM intake, that my Performer might be the choke and a Crower 60919 would be better than my current Summit 2802.


I really don't want to lose street manners, but would like more power when I punch it. Also, trying to keep the budget relatively low. I've already put so much money into this car.

Its not that 750 is to small, that Holley 750 vacuum secondary crab, Sucks !! Big time. Forgive me because I’m doing this for memory I’ve had to modify those crabs. Here’s why The secondaries are limited jetting wise. Been a while since I’ve done one, but out of memory The metering block Has to be changed in order to get the proper Jetting. When you put your foot into it its just not getting enough fuel and its going to feel like a dog. I would still definitely go with more cam though.

I would ditch that Holly, or get someone who knows how to modify them. Your much better off with a good 750 Q’jet.

Nope to perform RPMs not the choke point. Trust me. Another thing as far as timing chain goes. The Crower 60919 cam. Dot to Dot usually comes in at 106, thay say installed at 108. It’s actually 4 degrees advanced here’s why with chain stretch you’ll end up at 112. So if it cam in dot-dot at 106, you’ll end up at 110. Which makes that cam perfectly street able . So Crower when they design that cam anticipated chain stretch. So they really want it to end up around 110-112. So I wouldn’t worry about running a shorter timing set. Just put in a good Cloys timing gear set, I think they go for 150.00. Don’t buy the cheapet set.

So, my Performer is fine, don't need an RPM, do the 60919, lifters, and 60404 springs and put the cam in dot to dot with a new chain and it'll wake it up some?

Even going by Edelbrock’s own recommendations your darn close to what the Performer can handle in terms of CID and cam.
The Performer is incapable of producing more then 430 Hp unless you lower the plenum divider 3/4” all the way across the plenum or run a open 1” spacer and at that point your better served by the Performer RPM or the T2 depending on your gearing and converter.

I too am surprised you have not torn your 700R up yet!

This is for now a happy accident showing you how down on torque your 469 motor combo is.

I agree, once you get the motor making the power that it should your 3.73 gears will then really show you that there too much .

Thanks Steve. The 700R4 isn't stock. It was built for strength. So you're recommending the RPM intake? The 60919 cam? Crower Cam Saver Lifters? 68404 springs? That's a good combo that will wake it up?

Can you describe how the car responds from a standstill and floored?